Obs:When moving at any speed as a unit around a halted enemy tank it does not react until you move either in front of it or fire a shot (See youtube video below).

Des:AI tank commanders should randomly timed "scan horizon" and hear if a unit runs close to the tank. Being lucky when walking between random scans by AI tank commander should make the player lucky enough to move in on the tank, and for example plant a satchel.

I think this may be remedied with scripting, e.g. setting them to danger mode and giving them a waypoint with Guard order or a patrol area, i.e. creating some potential real life scenario.

I can't think of a real life example where a tank is just supposed to sit on a place with no order. Normally, if a tank crew is just e.g. waiting somewhere to meet up with friendly units, they're turned out or maybe even disembarked.